1. Field of the Invention
The present invention relates to a method of manufacturing a sole and a sole obtained by the method.
2. Description of the Background Art
Various types of materials for molding soles are known in the art. For example, Japanese Patent Laying-Open No. 8-294933 (1996) discloses a method of manufacturing a sole of a gym shoe by halogenating the surface of a rubber material and thereafter multicolor-molding the surface of the halogenated rubber material with a thermoplastic material such as a polyurethane elastomer or a polyamide elastomer by compression molding or injection molding.
In Japanese Patent Laying-Open No. 8-294933, however, effects of and conditions for halogenation of the rubber material with a chlorine-based primer or a bromine-based primer are not clearly described. The method according to Japanese Patent Laying-Open No. 8-294933 has not been put into practice, due to insufficient adhesive power.
Japanese Patent Laying-Open No. 7-195622 (1995) discloses a composite product prepared by bonding a thermoplastic material to a thermoplastic elastomer (TPV) obtained by dynamically vulcanizing rubber dispersed into a thermoplastic matrix as particulates, i.e., an article made of a thermoplastic material and TPV. Japanese Patent Laying-Open No. 7-195622 also discloses a method of molding a sole by injecting a TPV alloy (thermoplastic/rubber alloy) onto a sole of polyetheresteramide having high fatigue resistance, a low deformation hysteresis and excellent low-temperature resistance by insertion molding or two-color injection molding.
National Patent Publication Gazette No. 8-505333 (1996) discloses a sole consisting of a two-layer article of a composition containing a lightweight thermoplastic elastomer bonded onto a dense material made of a non-lightweight thermoplastic material selected from a group consisting of polyetheramide, polyetherester and polyurethane.
In the sole consisting of the two-layer article of the composition containing the lightweight thermoplastic elastomer bonded onto the dense material made of the non-lightweight thermoplastic material selected from the group consisting of polyetheramide, polyetherester and polyurethane disclosed in National Patent Publication Gazette No. 8-505333, however, durability of the sole itself may be reduced due to low durability of the lightweight thermoplastic elastomer itself.
National Patent Publication Gazette No. 8-511741 (1996) discloses a composite structure obtained by combining a vulcanized elastomer containing a carboxylic group with a thermoplastic polymer containing a block and a method of manufacturing a sole for a gym shoe by vulcanizing an elastomer on a thermoplastic polymer.
In National Patent Publication Gazette No. 8-511741, however, no specific method of manufacturing a sole is described in detail. If press molding is employed, for example, a flash (coat) of rubber is formed on the thermoplastic polymer, and the method cannot be put into practice in view of the appearance of the manufactured sole.
According to the aforementioned method of manufacturing a sole, further, a molding temperature exceeding a heat distortion temperature is applied to a thermoplastic elastomer sheet, and hence heat distortion and distortion in cooling remain after demolding. In order to prevent this, a molding die for injection-molding a bottom sole must be provided with a cooling apparatus, and hence extremely high-priced and complicated equipment is required. Thus, the method disadvantageously requires a high cost. In this regard, a sole and a method of manufacturing a sole with a material having excellent durability, proper hardness, flexibility, cushioning properties, traction properties and productivity and requiring a low cost have been awaited.
Japanese Patent Laying-Open No. 2000-41702 discloses a sole having a three-layer structure obtained by simultaneously integrally molding a rubber material made of a thermosetting elastic body and a bonding layer made of a thermoplastic elastomer and thereafter injection-molding a base portion made of a thermoplastic elastomer for forming the body of the sole and a method of manufacturing the sole having the three-layer structure.
In the sole having the three-layer structure disclosed in Japanese Patent Laying-Open No. 2000-41702, adhesion between the rubber material and the base portion is sufficiently improved due to the bonding layer interposed therebetween, and dispersion in adhesive power is remarkably reduced. However, the method disclosed in Japanese Patent Laying-Open No. 2000-41702 requires a mold die cooling step, and hence the manufacturing steps are complicated, to result in increase of the manufacturing cost.